Differential Positron Annihilation Spectroscopy in Nondestructive Testing of Thin Chromium Coatings on Copper

摘要

The differential positron annihilation spectroscopy (DPAS) is used for the nondestructive investigation of thin metallic coatings on metallic substrates when the defectiveness of the coating applied is judged from the difference between the spectra of the individual substrate and the substrate covered with the coating. Using the DPAS angular correlation curves of positron annihilation radiation (ACAR), the presence of nanoscale void clusters in the X-ray amorphous galvanic chromium coatings with a weight thickness of 9.15 mg/cm~2 (1.3 μm) is determined on the copper substrate. The ACAR curves of the coatings have a complex structure compared to those of the specimens of Cr_3C_2 and Cr_(23)C_6 carbide powders and involve a narrow peak with a half width FWHF = 3 mrad and an intensity about 2% assigned to void clusters with a size of 0.86 run, which act as positron traps, in the coating.